R503

Section R503 is titled 'Floor Sheathing' and covers the requirements for the thin structural members which rest on floor joists and rafters (including rafters which are pitched). Several tables provide prescriptive designs of different joist/rafter spacings and sheathing orientations (along with additional footnote details). The section primarily covers 3 types of sheathing - lumber, wood structural panels, and particleboard, but other types of underlayment are referenced in combined use with wood structural panels. Subflooring and 'combination subfloor underlayment' are structural, whereas standard underlayment is not structural and would be installed on top of structural subflooring. The purpose of this section is to provide structural stability.

The model displays several sections of floors and roofs with different spacing, sheathing, and underlayment.